Following a number of delays, the Mozilla Project has confirmed that it plans to ship the seventh beta for version 4 of its open source Firefox web browser on Wednesday, the 10th of November. This seventh beta for version 4 of Firefox 4 is the first beta to include the new Jaegermonkey javascript engine for Firefox.

" Well, it's still a beta release so there's a large chance that it still contains alot of debug code. Not until the final version is released will we know the exact performance. But the beta releases should give an indication. Weird that the GUI would be sluggish though, wasn't that supposed to be faster?

Nope. when they say faster, they mean the JS performance. There is a current war between browsers in terms of JS performance.
In terms of GUI, it's definitely slower. Menus are sluggish and switching tabs is a bit laggy. "

In terms of GUI, I can't get Firefox menus to be any more sluggish, or tabs any more laggy, than any other application on my system.